Deposits of oil sands are found around the world, but most prominently in Canada, Venezuela, and the United States, most significantly in Utah. These oil sands contain significant deposits of heavy oil, typically referred to as bitumen. The bitumen from these oil sands may be extracted and refined into synthetic oil or directly into petroleum products.
The difficulty with bitumen lies in that it typically is very viscous, sometimes to the point of being more solid than liquid. Thus, bitumen typically does not flow as less viscous, or lighter, crude oils do.
Because of the viscous nature of bitumen, it cannot be produced from a well drilled into the oil sands as is the case with lighter crude oil. This is so because the bitumen simply does not flow without being first heated, diluted, or upgraded.
Since normal oil drilling practices are inadequate to produce bitumen, several methods have been developed over several decades to extract and process oil sands to remove the bitumen. For shallow deposits of oil sands, a typical method includes surface extraction, or mining, followed by subsequent treatment of the oil sands to remove the bitumen.
The development of surface extraction processes has occurred most extensively in the Athabasca field of Canada. In these processes, the oil sands are mined, typically through strip or open pit mining with draglines, bucket-wheel excavators, and, more recently, shovel and truck operations. The oil sands are then transported to a facility to process and remove the bitumen from the sands. These processes typically involve a solvent of some type, most often water or steam, although other solvents, such as hydrocarbon solvents, have been used.
After excavation, a hot water extraction process is typically used in the Athabasca field in which the oil sands are mixed with water at temperatures ranging from approximately 110° F. to 180° F., with recent improvements lowering the temperature necessary to the lower portion of the range. A surfactant, such as sodium hydroxide (NaOH), or other surfactants, and air are also mixed with the oil sands.
Adding the water and NaOH to the oil sands creates a slurry, which is then transported to an extraction plant, typically via a pipeline. Inside a separation vessel, the slurry is agitated and the water and NaOH releases the bitumen from the oil sands. Air entrained with the water and NaOH attaches to the bitumen, allowing it to float to the top of the slurry mixture and create a froth. The bitumen froth is further treated to remove residual water and fines, which are typically small sand and clay particles. The bitumen is then either stored for further treatment or immediately treated, either chemically or mixed with lighter petroleum products, and transported by pipeline for upgrading into synthetic crude oil.
This process removes approximately 75% of the bitumen. Additional treatments applied to the oil sands may remove another 10% to 20% of the bitumen from the sands. The relatively clean sands (as compared to the oil sands) are then returned to the mine, typically in the form of tailing piles. Because some bitumen, NaOH, or other hazardous materials may remain on the relatively clean sands, the sands must be further treated or stored in tailings piles that have protections to prevent any of the hazardous materials from leaching into the ground or nearby water sources.
Another method of extracting bitumen from oil sands includes a hydrocarbon-based solvent extraction process in which a solvent or mixture of solvents flows counter-current to a slurry of oil sand and solvent in a processor. The solvent helps separate the bitumen from the sand and the solvent-bitumen mixture is drawn off from the top of the processor while sands with any remaining bitumen and solvent exit from the bottom of the processor.
While the known methods of extracting bitumen from oil sands work well with certain deposits of oil sands, those same processes often work poorly with deposits of oil sands that have different characteristics. For example, the processes that use water typically work poorly with oil sands that have a high concentration of clay mixed within the oil sands. The water may bind with the clay, causing the clay to swell and clog pipes, fittings, and other processing machinery. Further, a significant volume of water is required when used as a solvent, which may not always be available at a location because of permitting requirements or simply the arid nature of a region in which the oil sands are located. Large pits or basins to store water, both before and after use when the water is polluted with bitumen and other chemicals are often required. Air, water, and ground pollution concerns, not to mention the large space required, often make this unfeasible. In addition, any water used must be treated to remove impurities and other pollutants, which typically is an expensive process.
Hydrocarbon-based solvent extraction processes may not always be suitable for a variety of reasons, too. First, air quality concerns often limit the use of hydrocarbon solvents because the evaporation of those solvents adversely affects air quality. In addition, solvent processes typically cost significantly more because of the cost and the large volume of solvent required. Pollution concerns often require special handling and disposal of these solvents, including those solvents that remain on the sand after processing, to prevent air, water, and ground pollution.
Therefore, an environmentally sound method of extracting bitumen for oil sands is required that addresses the short comings in previous methods of processing oil sands.